Narcolepsy and 2009 H1N1 pandemic vaccination in Taiwan

Several European countries have observed an association between narcolepsy and H1N1 vaccines containing AS03® adjuvant in children/adolescents. In Taiwan, a nationwide campaign starting November 2009 administered H1N1 vaccines without adjuvant or with MF59® adjuvant to 67% of children and 12% of adults.

For those registered in the 2000-2012 National Health Insurance (NHI) databases, we compared age-stratified (0-4, 5-18, 19-59, and ≥60 years) incidence of first referral for a diagnostic MSLT for the pre-pandemic, pandemic/pre-vaccination, and vaccination/post-pandemic period. We also compared the odds of H1N1 vaccination in each chart-ascertained narcolepsy patient, whoever had an onset of excessive daytime sleepiness between April 2009 and December 2012, with 10 population-based controls from the NHI databases on year of birth, sex, and index date, using conditional logistic regressions.

Incidence of MSLT referral for narcolepsy was highest and significantly increased in the pandemic/pre-vaccination period in the age group 5-18 (IRR 3.40, 95% confidence intervals (CI) 2.12-5.45) and 19-59 (IRR 2.90, 95% CI 1.62-5.02) years. Among 137 confirmed narcolepsy cases (86 adults and 51 children), the odds ratios (ORs) were 1.67 (95% CI 0.81-3.45) (adults) and 1.22 (95% CI 0.62-2.39) (children) for H1N1 vaccination without adjuvant, and 1.39 (95% CI 0.17-11.48) (adults) and 3.66 (95% CI 0.37-36.02) (children) with MF59® adjuvant.

No substantial association between the use of H1N1 vaccines and narcolepsy was identified in Taiwan. Instead, the H1N1 infection itself could have played a role in triggering narcolepsy in children and young adults.